Asymmetric epoxidation catalyzed by D-glucose-derived uloses

Article abstract of DOI:10.1016/S0040-4020(02)00577-X

Three ulose catalysts (1-3) were prepared from D-glucose via an intramolecular nitrile oxide cycloaddition (INOC) as the key step. The enantioselectivity of ulose 2 and 3 in asymmetric epoxidation was poor (up to 26% ee). Ulose 1 afforded good chemical yields (up to 83% yield) and the enantiomeric excess is up to 71% for the formation of (-)-trans-stilbene oxide.

Full text of DOI:10.1016/S0040-4020(02)00577-X

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 7545±7552
Asymmetric epoxidation catalyzed by d-glucose-derived uloses
Tony K. M. Shingp and Gulice Y. C. Leung
Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong, People's Republic of China
Received 19 February 2002; revised 15 May 2002; accepted 6 June 2002
AbstractÐThree ulose catalysts (1±3) were prepared from d-glucose via an intramolecular nitrile oxide cycloaddition (INOC) as the key
step. The enantioselectivity of ulose 2 and 3 in asymmetric epoxidation was poor (up to 26% ee). Ulose 1 afforded good chemical yields(up
to 83% yield) and the enantiomeric excess is up to 71% for the formation of (2)-trans-stilbene oxide. q 2002 Elsevier Science Ltd. All rights
reserved.
1. Introduction
The syntheses of the ulose catalysts primarily follow the
reaction sequence developed earlier by us5 with some
modi®cations, and are shown in Schemes 1 and 2. The
intramolecular nitrile oxide cycloaddition (INOC) was
used as the key step to construct the isoxazolidines 10, 11
and 18. Hydrogenolysis of the isoxazolidines with Ra-Ni
and subsequent protection of the corresponding b-hydroxy-
ketones 12, 13, and 19 with TBDMSCl afforded uloses 1, 2,
and 3, respectively. The difference between 1 and 2 is
that for ulose 2, a methyl group occupiesthe a-position
relative to the ketone function. Thismethyl group hsould
impose signi®cant steric hindrance around the ketone
group in ulose 2, thereby affecting the asymmetric
induction of the epoxidation. For ulose 3, the pyranone
ring is trans-fused to the furanoid ring and the spatial orien-
tation of the exocyclic silyl ether is at the b-face of the
pyranone ring.
Dioxiranesare verastile epoxidizing agentsthat can be
generated in situ from oxone and a catalytic amount of
electrophilic ketones.1 In recent years, Yang,2 Shi3 and
other workers4 have developed elegant chiral ketonesand
applied them in asymmetric epoxidation, via their corre-
sponding dioxiranes. According to their studies, cyclic C2-
symmetry and fructose-derived ketones can function as
catalysts to afford chiral epoxides in high chemical yields
and enantiomeric excesses. Our long term interest in
employing carbohydrates in asymmetric synthesis has there-
fore initiated our search for ef®cient ulose catalysts that can
induce chirality with high ee in asymmetric epoxidation. In
this paper, we report our results on asymmetric epoxidation
catalyzed by d-glucose-derived uloses 1±3 (Fig. 1).
The relative stereochemistry of ulose 2 wascon®rmed by an
X-ray crystallographic analysis of its acetate derivative 14
(Fig. 2). The structure of ulose 3 wasalso con®rmed by an
X-ray crystallographic analysis (Fig. 3).
2. Results and discussion
d-Glucose was used as the starting material because it is
inexpensive and contains a number of stereogenic centers.
Figure 1. The structures of uloses 1±3 and of alkenes a±e.
Keywords: asymmetric epoxidation; ulose; d-glucose.
Corresponding author. Tel.: 1852-2609-6367; fax: 1852-2603-5057; e-mail: tonyshing@cuhk.edu.hk
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00577-X

7546
T. K. M. Shing, G. Y. C. Leung / Tetrahedron 58 (2002) 7545±7552
Scheme 1. Syntheses of uloses 1, 2, and 14. Key: (a) 4: (i) NaH, THF; (ii) allyl bromide; 5: (i) NaH, THF; (ii) 3-bromo-2-methylpropene; (b) 90% AcOH; (c) i)
NaIO4-silica gel,14 CH2Cl2; (ii) NH2OH´HCl, NaHCO3, EtOH, re¯ux; (d) 10% NaOCl, CH2Cl2, re¯ux; (e) Ra-Ni, H2, CH2Cl2/MeOH/AcOH (10:5:1, v/v); (f) 1
and 2: TBDMSCl, imidazole,CH2Cl2; 14: Ac2O, pyridine.
With the ulose catalysts in hand, we began our study on the
concentration effect of ulose 1 in CH3CN. The results are
summarized in Table 1. Ulose catalyst 1 showed moderate
catalytic activities (63% yield using 10 mol% catalyst) and
chiral induction (65% ee). The 1:10 ratio of catalyst to
substrate exhibited the similar results as 1:1 ratio of catalyst
to substrate, hinting at 10 mol% as the optimum concentra-
tion for the epoxidation. The optical rotation valuesof the
recovered catalysts were in close agreement to that of the
20
enantiopure 1 ([a]D ˆ137.4, c 0.8, CHCl3), thereby indi-
cating that epimerization did not occur during the epoxida-
tion, which would otherwise have affected the
enantioselectivity of the epoxidation. Having realised the
optimum concentration of catalyst as 10 mol%, we went
Scheme 2. Synthesis of ulose 3. Key: (a) (i) NaH, THF; (ii) allyl bromide; (b) 90% AcOH; (c) (i) NaIO4-silica gel,14 CH2Cl2; (ii) NH2OH´HCl, NaHCO3,
EtOH, re¯ux; (d) 10% NaOCl, CH2Cl2, re¯ux; (e) Ra-Ni, H2, CH2Cl2/MeOH/AcOH (10:5:1, v/v); (f) TBDMSCl, imidazole, CH2Cl2.

T. K. M. Shing, G. Y. C. Leung / Tetrahedron 58 (2002) 7545±7552
7547
Table 2. Asymmetric epoxidation catalyzed by uloses 1±3 in CH3CN
Entrya Catalysts Substrates Yield (%)b ee (%)c Con®guration
d
1
2
3
4
5
6
7
8
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
a
a
a
b
b
b
c
c
c
d
d
d
e
63
23
66
78
16
80
80
14
81
66
26
60
61
14
43
65
11
26
28
4
7
45
4
40
11
4
5
10
5
(2)-(S,S)7
(2)-(S,S)7
(2)-(S,S)7
(1)-(R,R)8
(1)-(R,R)8
(1)-(R,R)8
(2)-(S,S)9
(2)-(S,S)9
(2)-(S,S)9
(2)-(S,S)10
(2)-(S,S)10
(2)-(S,S)10
(2)-(S)11
9
10
11
12
13
14
15
Figure 2. Molecular structure of ulose 14 (CCDC no. 183919). Thermal
ellipsoids are drawn at 20% probability level.
e
e
(2)-(S)11
3
(2)-(S)11
a
All reactions were carried out at room temperature with substrate
(0.1 mmol), ketone (0.01 mmol) at pH 7 for 2.5 h.
Isolated yield.
b
c
1
Enantioselectivity was determined by H NMR analysis of the epoxide
productsdirectly with shift reagent Eu(hfc)
.
3
d
The absolute con®gurations were determined by comparing the measured
optical rotationswith the reported ones.
trans-stilbene catalyzed by ulose 1 isused asan example
(Fig. 4). The well-established spiro transition state6 isused
to explain the predominant formation of the (S,S)-stilbene
oxide. Fig. 4 shows all the possible transition states (TS) and
the corresponding stereochemistry of the stilbene oxides.
TS-3 and TS-4 experience steric interaction between the
phenyl group in alkene and the silyl blocking group or the
furanose ring of ulose 1, respectively. Therefore, (R,R)-
stilbene oxide was not favored to form. In contrast, TS-1
and TS-2 have no such interaction, (S,S)-stilbene oxide
becomesthe dominant product. Similar resultsare obtianed
for alkene c. For alkenes b, d and e, the steric effects for
TS-3 and TS-4 are reduced and hence the formation of
(R,R)-epoxide increased, leading to poor enantioselectivity.
The poor ee results (3±40% ee) for ulose catalysts 2 and 3
indicate that the silyl blocking groups and the furanose ring
could not impose suf®cient steric interaction to induce
chirality with high ee's(Fig. 4).
Figure 3. Molecular structure of ulose 3 (CCDC no. 183918). Thermal
ellipsoids are drawn at 20% probability level.
Table 1. Concentration effect of ulose 1 in catalyzing in situ epoxidation of
trans-stilbene in CH3CN
Entrya Mol% of 1 Yield (%)b ee (%)c [a]D20 of recovered catalystd
1
2
3
10
50
100
63
66
64
65
64
66
137.1, c 0.3, CHCl3
136.8, c 1.7, CHCl3
137.3, c 3.5, CHCl3
a
Reaction conditions: rt, 0.1 mmol of trans-stilbene at pH 7 for 2.5 h (entry
1); 1 h (entry 2); 0.5 h (entry 3).
Isolated yield from column chromatography.
Enantiomeric excess (ee) was determined by 1H NMR with shift reagent
Eu(hfc)3.
b
c
To improve the catalytic featuresof uloes catalyts
1, the
d
Catalyst was recovered from column chromatography.
solvent effect and the catalyst concentration effect were
investigated. The results are summarized in Tables 3 and
4. Among the solvents tested (Table 3), the mixture of
acetonitrile and diglyme in a ratio of 3:2 (v/v) (entry 9)
wasfound to be the solvent of choice for better reactivity
and selectivity. In addition, the results in Table 4 show that
5±10 mol% wasthe optimum catalyst concentration (entries
4 and 5). Using the ®ne-tuned reaction conditions, the asym-
metric epoxidation using ulose 1 wasfurther studied and the
results are summarized in Table 5. The chemical yields and
enantioselectivity were improved slightly (up to 20% yield
and up to 10% ee increase).
on to study the asymmetric epoxidation of alkenes a±e
using uloses 1±3 at thisconcentration (Fig. 1). The results
are summarized in Table 2. Uloses 1 and 3 afforded better
chemical yields (43±80% yields) than ulose 2 (26% yield at
best) and all the ulose catalysts were recovered without
decomposition. This shows that ulose 2 isnot an ef®cient
catalyst. Ulose 1 displayed better enantioselectivity than
uloses 2 and 3 (Table 2, entries1, 4, 7 and 13). The best
ee was65% for trans-stilbene oxide (Table 2, entry 1), but
poor ee'swere obtained for other alkenes(Table 2, entries4,
7, 10 and 13).
In conclusion, ulose 1 gave good reactivity towardsthe
epoxidation (63±80%) but the enantioselectivity was poor
for various alkenes. The poor stereochemical communica-
tion between the catalyst 1 and substrates caused us to
design new ulose catalysts for asymmetric epoxidation.
The research in this direction is in progress.
Examination of molecular modelscan provide better under-
standing to the stereochemical outcome of the dioxirane
epoxidation and suggest explanation for the poor enantio-
selectivity results of other alkenes. The epoxidation of

7548
T. K. M. Shing, G. Y. C. Leung / Tetrahedron 58 (2002) 7545±7552
Figure 4. The spiro transition states for trans-stilbene epoxidation catalyzed by ulose 1.
Table 3. Solvent effect on asymmetric epoxidation of trans-stilbene catalyzed by ulose 1
Entrya
Solvent
Yield (%)b
ee (%)c
Con®guration d
1
CH3CN
CH3CN
63
23
80
82
69
20
0
65
0
(2)-(S,S)
±
2e
3
CH3CN/DME (4:1, v/v)
CH3CN/DME (3:2, v/v)
CH3CN/DME (2:3, v/v)
CH3CN/DME (1:4, v/v)
DME
51
60
41
25
±
(2)-( S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
±
4
5
6
7
8
9
CH3CN/Diglyme (4:1, v/v)
CH3CN/Diglyme (3:2, v/v)
CH3CN/Diglyme (2:3, v/v)
CH3CN/Diglyme (1:4, v/v)
Diglyme
Diglyme/DME (4:1, v/v)
Diglyme/DME (3:2, v/v)
Diglyme/DME (2:3, v/v)
Diglyme/DME (1:4, v/v)
86
80
84
69
47
68
44
17
0
58
71
66
62
65
66
61
63
±
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
±
10
11
12
13
14
15
16
a
All reactions were carried out at room temperature with substrate (0.1 mmol), ketone (0.01 mmol) at pH 7 for 2.5 h.
Isolated yield.
Enantioselectivity was determined by chiral HPLC (Chiralcel OD); eluant: (9:1 hexane/IPA, v/v); retention time: 5.7 and 8.6 min.
The absolute con®gurations were determined by comparing the measured optical rotations with the reported ones.7
Reaction wascarried out without catalyst for 24 h.
b
c
d
e
3. Experimental
ethanol and subsequent heating. E. Merck silica gel 60
(230±400 mesh) was used for ¯ash chromatography. All
reagentsand oslventswere general reagent grade unles
otherwise stated. Other reagents were purchased from
commercial suppliers and were used without puri®cation.
Melting pointswere measured with a Reichert apparatusin
Celsius degrees and are uncorrected. NMR spectra were
measured with a Bruker DPX300 NMR spectrometer at
300.13 MHz (1H) or at 75.47 MHz (13C) in CDCl3, unless
stated otherwise. Elemental analyses were carried out by
MEDAC Ltd, Department of Chemistry, Brunel University,
Uxbridge, UK. All reactionswere monitored by analytical
thin-layer chromatography (TLC) on Merck aluminum-
3.1. General in situ epoxidation procedure at pH 7±7.5
To a stirred solution of substrate (0.1 mmol), ketone
(0.01 mmol) and n-Bu4NHSO4 (0.5 mg) in solvent (5 mL)
and aqueousoslution (1 mL, 4 £1024 M aqueousEDTA)
were added dropwise a solution of oxone (1 mmol) in
precoated platesof islica gel 60 F
spraying with 5% (w/v) dodecamolybdophosphoric acid in
with detection by
254

T. K. M. Shing, G. Y. C. Leung / Tetrahedron 58 (2002) 7545±7552
7549
1
hexane, 1:1); nmax(CHCl3) 1470 (CvC) cm21; H NMR d
5.88 (1H, d, Jˆ3.9 Hz); 5.97±5.81 (1H, m), 5.30 (1H, dt,
Jˆ17.3, 1.5 Hz), 5.19 (1H, dt, Jˆ10.4, 1.4 Hz), 4.53 (1H, d,
Jˆ3.7 Hz), 4.30 (1H, q, Jˆ4.3 Hz), 4.14±3.92 (6H, m),
1.48, 1.43, 1.35 and 1.30 (4£Me, s); MS (EI) m/z 285
(M12Me, 40.6).
Table 4. Catalyst concentration effect for asymmetric epoxidation of trans-
stilbene catalyzed by ulose 1 in CH3CN/diglyme (3:2)
d
Entrya
Mol%
Yield (%)b
ee (%)c
Con®guration
1
2
3
4
5
6
7
100
50
25
10
5
82
79
81
80
76
76
41
72
69
71
71
66
64
57
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
(2)-(S,S)
3.1.2.
3-O-(20-Methyl-20-propenyl)-1,2:5,6-di-O-iso-
2
1
propylidene-a-d-glucofuranose (5). Sodium hydride
(60%, 0.22 g, 5.7 mmol) was suspended in dry THF
(5 mL) under nitrogen at 08C. A solution of 1,2:5,6-di-O-
isopropylidene-a-d-glucofuranose13 (1.00 g, 3.8 mmol) in
THF (20 mL) was added dropwise using a dropping funnel
and the mixture wastsirred for 1/2 h at rt. 3-Bromo-2-
methylpropene (0.74 mL, 8 mmol) wasadded lsowly at
08C. The mixture washeated under re¯ux for 6 h. Saturated
NH4Cl wasadded very slowly at 0 8C and the solution was
extracted with CHCl3 (3£50 mL), dried over anhydrous
MgSO4, and ®ltered. The ®ltrate wasconcentrated to give
compound 5 as a yellow syrup that was used in the next
stage without puri®cation (1.04 g, 87%): Rf 0.45 (Et2O/
a
All reactions were carried out at room temperature with substrate
(0.1 mmol), ketone at pH 7 for 2.5 h.
Isolated yield.
b
c
Enantioselectivity was determined by chiral HPLC (Chiralcel OD) eluent:
(9:1 hexane/IPA, v/v); retention time: 5.7 and 8.6 min.
The absolute con®gurations were determined by comparing the measured
d
7
optical rotationswith the reported ones.
Table 5. Asymmetric epoxidation catalyzed by ulose 1 in CH3CN/diglyme
(3:2)
1
Entrya
Substrates
Yield (%)b
ee (%)c
Con®guration d
hexane, 1:4); H NMR d 5.82 (1H, d, Jˆ3.6 Hz), 4.93
(1H, s), 4.85 (1H, s), 4.48 (1H, d, Jˆ3.6 Hz), 4.27 (1H, q,
Jˆ6 Hz), 4.07±3.87 (6H, m), 1.69, 1.43, 1.36, 1.28 and 1.25
(5£Me, s); 13C NMR d 141.4, 112.7, 111.5, 108.8, 105.1,
82.3, 81.1, 80.9, 73.9, 72.2, 67.2, 26.7, 26.6, 26.1, 25.2,
19.2; MS (FAB) m/z 315 (M11H, 36), 299 (100), 257 (31).
1
2
3
4
5
a
b
c
d
e
80
77
83
80
63
71
29
47
22
23
(2)-(S,S)7
(1)-(R,R)8
(2)-(S,S)9
(2)-(S,S)10
(2)-(S)11
a
All reactions were carried out at room temperature with substrate
(0.1 mmol), ketone (0.01 mmol), oxone (1 mmol) at pH 7 for 2.5 h.
Isolated yield.
3.1.3. 3-O-Allyl-1,2-O-isopropylidene-a-d-glucofuranose
(6).5 Diacetonide 4 (1.00 g, 3.3 mmol) was dissolved in 90%
aqueous acetic acid (30 mL) and the resulting solution was
stirred for 24 h at rt. The solution was concentrated to give a
crude syrup which was ¯ash chromatographed on silica gel
(Et2O/hexane, 3:1) to yield diol 6 (0.83 g, 95%) asa pale
b
c
1
Enantioselectivity was determined by H NMR analysis of the epoxide
.
productsdirectly with shift reagent Eu(hfc)
The absolute con®gurations were determined by comparing the measured
optical rotationswith the reported ones.
3
d
23
yellow syrup: Rf 0.48 (Et2O/hexane, 3:1); [a]D ˆ245 (c 1,
aqueousEDTA (3 mL, 4 £1024 M) and a solution of
NaHCO3 (3.1 mmol) in H2O (3 mL) concomitantly via
two dropping funnels. The pH of the mixture was main-
tained at about 7±7.5 over a period of 2.5 h. The reaction
mixture wasthen poured into water (10 mL), extracted with
CHCl3 (3£10 mL), dried with anhydrousmagneiusm
sulfate, and ®ltered. The ®ltrate was concentrated under
reduced pressure to give a residue that was puri®ed by
¯ash column chromatography to give the epoxide. Enantio-
CHCl3) (lit.,5 [a]D ˆ246 (c 1.6, CHCl3)); nmax(CHCl3)
23
3425 (OH) cm21; H NMR d 5.87 (1H, d, Jˆ3.8 Hz),
1
5.92±5.79 (1H, m), 5.28 (1H, dd, Jˆ17.4, 1.1 Hz), 5.18
(1H, dd, Jˆ10.3, 10 Hz), 4.51 (1H, d, Jˆ3.8 Hz), 4.16±
3.91 (5H, m), 3.71 (2H, qd, Jˆ11.5, 3.2 Hz), 1.45, 1.27
(2£Me, s), MS (EI) m/z 245 (M12Me, 6.7).
3.1.4. 3-O-(20-Methyl-20-propenyl)-1,2-O-isopropylidene-
a-d-glucofuranose (7). Selective deprotection of the termi-
nal acetonide in 5 (2.00 g, 6.3 mmol) in a similar manner as
in the preparation of diol 6 gave diol 7 (1.50 g, 87%) asa
1
selectivity was determined by H NMR analysis of the
epoxide directly with shift reagent Eu(hfc)3 at the NMR
signal 3.8±4.1 ppm.
23
colorless syrup: Rf 0.52 (EtOAc/hexane, 2:1); [a]D ˆ25.9
1
(c 1.0, CHCl3); nmax(CHCl3) 3410 (OH) cm21; H NMR d
3.1.1. 3-O-Allyl-1,2:5,6-di-O-isopropylidene-a-d-gluco-
furanose (4).12 Sodium hydride (60%, 0.70 g, 17.4 mmol)
was suspended in dry THF (5 mL) under nitrogen at 08C. A
solution of 1,2:5,6-di-O-isopropylidene-a-d-glucofura-
nose13 (3.00 g, 11.6 mmol) in THF (30 mL) wasadded
dropwise using a dropping funnel and the mixture was stir-
red for 1/2 h at rt. Allyl bromide (2.2 mL, 24 mmol) was
added slowly at 08C. The mixture washeated under re¯ux
for 6 h. Saturated NH4Cl wasadded very slowly at 0 8C and
the solution was extracted with CHCl3 (3£50 mL), dried
over anhydrousMgSO 4, and ®ltered. The ®ltrate was
concentrated to give a yellow syrup. The crude syrup was
puri®ed by ¯ash chromatography to allyl ether 4 asa yellow
5.87 (1H, d, Jˆ3.6 Hz), 4.96 (1H, s), 4.88 (1H, s), 4.54 (1H,
d, Jˆ3.9 Hz), 4.10±3.91 (5H, m), 3.79 (1H, dd, Jˆ11.4,
3.3 Hz), 3.68 (1H, dd, Jˆ11.4, 5.4 Hz), 3.09 (2H, s), 1.72,
1.45, 1.28 (3£Me, s); 13C NMR d 141.3, 112.8, 111.6,
104.9, 81.9, 81.8, 79.8, 74.0, 69.0, 64.2, 26.6, 26.1, 19.5;
MS (FAB) m/z 275 (M11H, 77), 217 (100), 199 (37). Anal.
calcd for C13H22O6: C, 56.92; H, 8.08. Found: C, 56.81; H,
7.95.
3.1.5.
3-O-Allyl-1,2-O-isopropylidene-a-d-arabino-
pentodialdo-1,4-furanose oxime (8).5 To a vigorously stir-
red suspension of silica gel supported NaIO4 reagent14
(2.00 g) in CH2Cl2 (5 mL) in a 25 mL round bottom ¯ask
wasadded a solution of the diol 7 (310 mg, 1.2 mmol) in
CH2Cl2 (5 mL). The reaction wasmonitored by TLC until
23
syrup (3.20 g, 92%): [a]D ˆ225 (c 1.1, CHCl3) (optical
12
rotation wasnot reported previoulsy)
Rf 0.57 (Et2O/

7550
T. K. M. Shing, G. Y. C. Leung / Tetrahedron 58 (2002) 7545±7552
disappearance of the starting material (about 30 min). The
mixture was ®ltered through a sintered glass funnel, and the
silica gel was thoroughly washed with CHCl3 (3£10 mL).
Removal of solvent from the ®ltrate afforded the crude alde-
hyde that was used in the next stage without puri®cation.
NH4OH´HCl, (153 mg, 2.20 mmol) and then NaHCO3
(185 mg, 2.20 mmol) were added to a solution of the alde-
hyde (251 mg, 1.10 mmol) in ethanol (25 mL). The reaction
mixture washeated under re¯ux for 1.5 h. The cooled
mixture wasconcentrated under reduced presure and the
residue subjected to silica gel ®ltration with eluant (EtOAc/
hexane, 1:1) to afford colorless needles 8 (recrystallization
from hexane/ether) asa mixture of Z/E isomer (2:1 respec-
isoxazoline 10 gave isoxazoline 11 (107 mg, 72%) asa
white solid. Recrystallization from hexane/EtOAc gave
white prisms: Rf 0.47 (hexane/EtOAc, 1:1); mp 104±
23
1
1068C; [a]D ˆ161.8 (c 2.8, CHCl3); H NMR d 5.96
(1H, d, Jˆ3.6 Hz), 4.91 (1H, d, Jˆ2.1 Hz), 4.60 (1H, d,
Jˆ3.3 Hz), 4.18 (1H, d, Jˆ8.4 Hz), 3.95 (1H, d,
Jˆ1.8 Hz), 3.92 (1H, d, Jˆ10.8 Hz), 3.89 (1H, d,
Jˆ8.4 Hz), 3.41 (1H, d, Jˆ10.8 Hz), 1.50 (3H, s), 1.40
(3H, s), 1.32 (3H, s); MS (FAB) m/z 256 (M11H, 100),
240 (15), 198 (11). Anal. calcd for C12H17O5N: C, 56.46;
H, 6.71; N, 5.48. Found: C, 56.54; H, 6.75; N, 5.42.
3.1.9. b-tert-Butyldimethylsilyloxy-ulose 1. To a solution
of isoxazoline 10 (150 mg, 0.5 mmol) containing 3 mol%
equivalent of acetic acid in CH2Cl2/methanol/water (10 mL,
10:5:1) wasadded a catalytic amount (10 mg) of Raney-Ni.
The system was evacuated and purged three times with H2
using a 3-way stopcock with a H2 balloon. The mixture was
then stirred vigorously under H2 (balloon) at 258C for 3 h.
CH2Cl2 (20 mL) wasadded, and the solution wasthen dried
over anhydrousMgSO 4, and ®ltered. The ®ltrate was
concentrated under reduced pressure to give b-hydroxy-
ulose 12 that was used in the next stage without puri®cation.
To a solution of the hydroxy-ulose 12 in dry CH2Cl2
(10 mL), were added imidazole (68 mg, 1.0 mmol),
TBDMSCl (90 mg, 0.6 mmol), and a catalytic amount
(5 mg) of DMAP. The mixture wastsirred at rt for 12 h
and then waspoured into asturated NH 4Cl (10 mL). The
aqueousphase wasextracted with CH 2Cl2 (3£10 mL) and
the combined organic extractswere wahsed with brine
(10 mL), dried (MgSO4), and ®ltered. Concentration of the
®ltrate followed by ¯ash chromatography (Et2O/hexane,
1:4) gave a white solid which was recrystallized from
EtOAc/hexane to give ulose 1 (97 mg, 54%) aswhite
crystals: Rf 0.50 (Et2O/hexane, 1:1); mp 76±778C;
1
tively, determined by H NMR) (247 mg, 80%): Rf 0.47
23
(EtOAc/hexane, 1:1); mp 89±918C; [a]D ˆ245 (c 1,
CHCl3) (lit.,5 mp 90±918C; [a]D ˆ246 (c 1.6, CHCl3));
23
1H NMR d 7.50 (0.3H, d, Jˆ7.4 Hz), 6.86 (0.6H, d,
Jˆ4.0 Hz), 5.92 (1H, d, Jˆ3.6 Hz), 5.82±5.68 (1H, m),
5.25±5.09 (3H, m), 4.54 (1H, dd, Jˆ5.2, 3.7 Hz), 4.00±
3.91 (3H, m), 1.44 (3H, s), 1.26 (3H, s); MS (EI) m/z 257
(M1, 2.3).
3.1.6. 3-O-(20-Methyl-20-propenyl)-1,2-O-isopropylidene-
a-d-arabino-pentodialdo-1,4-furanose
oxime
(9).
Conversion of the diol 7 (1.46 g, 5.33 mmol) in a similar
manner asin the preparation of oxime 8 gave oxime 9
(1.25 g, 91%) ascolorlesneedles(recrytsallization from
hexane/ether) asa mixture of Z/E isomer (1:1 respectively,
determined by 1H NMR): Rf 0.55 (EtOAc/hexane, 1:1); mp
23
80±828C; [a]D ˆ2147.6 (c 1.3, CHCl3); nmax(CHCl3)
1
3375 (OH) cm21; H NMR d 7.51 (0.53H, d, Jˆ7.5 Hz),
6.96 (0.5H, d, Jˆ3.9 Hz), 5.99 (1H, t, Jˆ3.6 Hz), 5.24
(0.5H, t, Jˆ3.6 Hz), 4.95 (1H, s), 4.92 (1H, d, Jˆ7.2 Hz),
4.76 (0.5H, dd, Jˆ7.5, 3.3 Hz), 4.61 (1H, t, Jˆ4.2 Hz), 4.31
(0.5H, d, Jˆ3.3 Hz), 4.02±3.87 (2.4H, m), 1.71 (3H, s), 1.52
(3H, s), 1.34 (3H, s); 13C NMR d 149.7, 147.9, 141.2, 140.9,
113.3, 112.1, 112.0, 105.3, 104.8, 83.2, 82.7, 82.4, 82.1,
77.8, 75.5, 74.3, 74.1, 26.8, 26.2, 19.3; MS (FAB) m/z 258
(M11H, 100), 242 (17), 200 (42). Anal. calcd for
C12H19O5N: C, 56.02; H, 7.44; N, 5.44. Found: C, 56.10;
H, 7.52; N, 5.44.
23
[a]D ˆ137.4 (c 0.8, CHCl3); nmax(CHCl3) 1716 (CvO)
1
cm21; H NMR d 6.04 (1H, d, Jˆ3 Hz), 4.62 (1H, d,
Jˆ3.6 Hz), 4.40 (1H, dd, Jˆ11.1, 6.3 Hz), 4.27 (1H, d,
Jˆ2.0 Hz), 4.21 (1H, d, Jˆ2.0 Hz),3.93 (1H, dd, Jˆ11.4,
4.1 Hz), 3.66 (1H, dd, Jˆ11.1, 8.2 Hz), 3.48 (1H, t,
Jˆ11.4 Hz), 3.19 (1H, m), 1.49 (3H, s), 1.31 (3H, s), 0.86
(9H, s), 0.04 (6H, s); 13C NMR d 203.9, 113.4, 107.1, 84.8,
84.4, 81.3, 70.9, 59.1, 49.8, 27.4, 26.9, 26.4, 24.8, 24.9;
MS (FAB) m/z 382 (M11Na, 2), 359 (M11H, 81), 301
(100), 243 (45). Anal. calcd for C17H30O6Si: C, 56.95; H,
8.43. Found: C, 56.90; H, 8.60.
3.1.7. Isoxazoline 10.5 To a solution of oxime 8 (128 mg,
0.53 mmol) in CH2Cl2 (50 mL), wasadded 10% aqueous
NaOCl (3.30 mL, 5.5 mmol) and the resulting solution
washeated under re¯ux for 10 h. The cooled solution was
extracted with CH2Cl2 (3£20 mL). The combined organic
extractswere dried over anhydrousMgSO 4, and ®ltered.
The ®ltrate was concentrated under reduced pressure and
the crude residue was puri®ed by ¯ash chromatography
(hexane/Et2O, 2:1) to afford the isoxazoline 10 asa white
solid (124 mg, 92%). Recrystallization from hexane/acetone
gave colorless prisms: Rf 0.35 (hexane/Et2O, 2:1); mp 125±
3.1.10. b-tert-Butyldimethylsilyloxy-ulose 2. Conversion
of isoxazoline 11 (210 mg, 0.82 mmol) in a similar manner
asin the preparation of ulose 1 gave ulose 2 (152 mg, 50%)
23
asa syrup: Rf 0.50 (Et2O/hexane, 1:2); [a]D 1 ˆ214.9 (c 8.3,
CHCl3); nmax(CHCl3) 1715 (CvO) cm21; H NMR d 5.99
(1H, d, Jˆ3.6 Hz), 4.65 (1H, d, Jˆ3.6 Hz), 4.29 (1H, d,
Jˆ2.7 Hz), 4.22 (1H, d, Jˆ3.0 Hz), 3.84±3.80 (3H, m),
3.39 (1H, d, Jˆ9.9 Hz), 1.57 (3H, s), 1.49 (3H, s), 1.22
(3H, s), 0.85 (9H, s), 0.02 (6H, d, Jˆ2.4 Hz); 13C NMR d
205.1, 112.6, 105.7, 84.3, 83.2, 79.5, 73.3, 65.2, 50.2, 26.9,
26.4, 25.8, 19.6, 18.1, 25.7; MS (FAB) m/z 373 (M11H,
47), 357 (29), 315 (100). Anal. calcd for C18H32O6Si: C,
58.03; H, 8.66. Found: C, 58.34; H, 8.98.
23
1268C; [a]D ˆ117 (c 0.7, CHCl3) (lit.,5 mp 124.5±1258C;
23
1
[a]D ˆ117 (c 1.0, CHCl3)); H NMR d 5.99 (1H, d,
Jˆ3.6 Hz), 4.99 (1H, d, Jˆ1.7 Hz), 4.59 (1H, d,
Jˆ3.6 Hz), 4.53 (1H, dd, Jˆ10.8, 8.7 Hz), 4.21 (1H, dd,
Jˆ10.8, 6.3 Hz), 4.00 (1H, d, Jˆ1.7 Hz), 3.87 (1H, t,
Jˆ9.0 Hz), 3.72±3.59 (1H, m), 3.31 (1H, t, Jˆ10.8 Hz),
1.54 (3H, s), 1.21 (3H, s); MS (EI) m/z 255 (M1, 0.7).
3.1.8. Isoxazoline 11. Conversion of oxime 9 (149 mg,
0.58 mmol) in a similar manner as in the preparation of
3.1.11. b-Acetoxy-ulose 14. To a solution of isoxazoline 11
(68 mg, 0.27 mmol) in CH2Cl2/methanol/AcOH (10 mL,

T. K. M. Shing, G. Y. C. Leung / Tetrahedron 58 (2002) 7545±7552
7551
10:5:1) wasadded a catalytic amount (10 mg) of Raney-Ni.
The system was evacuated and purged three times with H2
using a 3-way stopcock with a H2 balloon. The mixture was
then stirred vigorously under H2 (balloon) at 258C for 3 h.
CH2Cl2 (20 mL) wasadded, and the solution wasthen dried
(1H, dd, Jˆ16.3, 1.4 Hz), 4.64 (1H, t, Jˆ4.0 Hz), 4.25
(1H, ddt, Jˆ12.3, 4.5, 1.0 Hz), 4.10±4.01 (3H, m), 3.92
(1H, dd, Jˆ8.6, 4.2 Hz), 3.94±3.89 (2H, m), 1.58, 1.36
(2£Me, s); MS (EI) m/z 245 (M12Me, 16.2). Anal. calcd
for C12H20O6: C, 55.37; H, 7.74. Found: C, 55.17; H, 7.66.
over anhydrousMgSO
and ®ltered. The ®ltrate was
4
concentrated under reduced pressure to give b-hydroxy-
ulose 13 that was used in the next stage without puri®cation.
To a solution of b-hydroxy-ulose 13 in dry CH2Cl2 (5 mL),
acetic anhydride (Ac2O) (43 mL, 0.46 mmol), pyridine
(1 mL), and a catalytic amount (5 mg) of DMAP were
added. The reaction mixture wastsirred at rt and then
quenched with saturated NH4Cl (10 mL). The aqueous
phase was extracted with CH2Cl2 (3£30 mL) and the
combined organic extractswere whased with brine
(2£5 mL), dried (MgSO4), and ®ltered. Concentration of
the ®ltrate followed by ¯ash column chromatography
(hexane/Et2O, 2:1) yielded the b-acetoxy-ulose 14 (69 mg,
86% from 11) aswhite crystals: Rf 0.52 (Et2O/hexane, 1:1);
3.1.14. 3-O-Allyl-1,2-O-isopropylidene-a-d-xylo-pento-
dialdo-1,4-furanose oxime (17). To a vigorously stirred
suspension of silica gel supported NaIO4 reagent14
(2.70 g) in CH2Cl2 (5 mL) in a 25 mL round bottom ¯ask
wasadded a solution of the diol 16 (2.19 g, 8.4 mmol) in
CH2Cl2 (5 mL). The reaction wasmonitored by TLC until
disappearance of the starting material (about 30 min). The
mixture was ®ltered through a sintered glass funnel, and the
silica gel was thoroughly washed with CHCl3 (3£10 mL).
Removal of solvent from the ®ltrate afforded the aldehyde
that was used in the next stage without puri®cation.
NH4OH´HCl, (1.72 g, 24 mmol) and then NaHCO3
(3.11 g, 29 mmol) were added to a solution of aldehyde in
ethanol (25 mL). The reaction mixture washeated under
re¯ux for 1.5 h. The solvent was removed under reduced
pressure and the residue subjected to silica gel ®ltration
with eluant (EtOAc/hexane, 1:2) to afford colorless needles
17 (recrystallization from hexane/ether) as a mixture of Z/E
isomer (10:1 respectively, determined by 1H NMR) (1.25 g,
60% from 16): Rf 0.45 (EtOAc/hexane, 1:1); mp 117±
1198C; [a]D ˆ2108 (c 0.1, CHCl3); H NMR d 7.32
(0.9H, d, Jˆ6.6 Hz), 7.2 (0.2H, s), 6.68 (0.1H, d,
Jˆ6.7 Hz), 5.92±5.77 (1H, m), 5.73 (1H, d, Jˆ3.6 Hz),
5.23 (1H, d, Jˆ11.6 Hz), 5.18 (1H, d, Jˆ10.4 Hz), 4.58
(1H, t, Jˆ3.9 Hz), 4.51 (1H, dd, Jˆ9.0, 6.6 Hz), 4.15±
4.00 (1H, m), 3.70 (1H, dd, Jˆ9.0, 4.3 Hz), 1.55 (3H, s),
1.30 (3H, s); MS (EI) m/z 228 (M12Me, 3.2). Anal. calcd
for C11H17O5N: C, 54.31; H, 7.04; N, 5.76. Found: C, 54.10;
H, 6.93; N, 5.70.
23
mp 112±1138C; [a]D ˆ23.4 (c 8.4, CHCl3); nmax(CHCl3)
1718 (CvO) cm21; 1H NMR d 5.99 (1H, d, Jˆ3.6 Hz), 4.64
(1H, d, Jˆ3.3 Hz), 4.29 (1H, d, Jˆ1.8 Hz), 4.27 (1H, d,
Jˆ7.2 Hz), 4.21 (1H, d, Jˆ2.4 Hz), 3.91 (1H, d,
Jˆ11.4 Hz), 3.79 (1H, d, Jˆ12.0 Hz), 3.70 (1H, d,
Jˆ12 Hz), 2.00 (3H, s), 1.46 (3H, s), 1.26 (6H, s); 13C
NMR d 202.8, 170.4, 112.6, 105.7, 83.9, 83.3, 79.3, 72.6,
65.2, 48.3, 26.7, 26.3, 20.6, 19.6; MS (FAB) m/z 301
(M11H, 86), 285 (41), 243 (69), 182 (100). Anal. calcd
for C14H20O7: C, 55.99; H, 6.71. Found: C, 55.91; H, 6.73.
23
1
3.1.12. 3-O-Allyl-1,2:5,6-di-O-isopropylidene-a-d-allo-
furanose (15). Sodium hydride (60%, 0.25 g, 6.3 mmol)
was suspended in dry THF (5 mL) under nitrogen at 08C.
A solution of 1,2:5,6-di-O-isopropylidene-a-d-allofura-
nose15 (1.10 g, 4.2 mmol) in THF (10 mL) wasadded drop-
wise using a dropping funnel and the mixture was stirred for
1/2 h at rt. Allyl bromide (0.55 mL, 6 mmol) wasadded
slowly at 08C. The mixture washeated under re¯ux for
6 h. Saturated NH4Cl solution was added very slowly at
08C and the solution was extracted with chloroform
(3£50 mL), dried over anhydrousMgSO 4, and ®ltered.
The ®ltrate wasconcentrated to give a yellow syrup which
was¯ash chromatographed to yield allyl ether 15 asa syrup
3.1.15. Isoxazoline 18. To a solution of oxime 17 (194 mg,
0.75 mmol) in CH2Cl2 (30 mL), 10% NaOCl (3.3 mL,
5.5 mmol) wasadded and left to heat under re¯ux for
10 h. The product wasextracted with CH Cl2 (3£20 mL).
2
The combined organic extractswere dried over anhydrous
MgSO4, and ®ltered. The solvent was removed from the
®ltrate under reduced pressure. The crude residue was puri-
®ed by ¯ash chromatography (hexane/EtOAc, 1:1) to afford
23
(1.10 g, 86%): Rf 0.45 (Et2O/hexane, 1:1); [a]D ˆ196 (c
1
1.1, CHCl3; nmax(CHCl3) 1456 (CvC) cm21; H NMR d
the isoxazoline 18 asa ysrup (115 mg, 64%):
Rf 0.32
(hexane/EtOAc, 1:1); [a]D ˆ161 (c 1.0, CHCl3); 1H
NMR d 5.87 (1H, d, Jˆ2.9 Hz), 4.71 (1H, t, Jˆ3.3 Hz),
4.49 (2H, dd, Jˆ17.5, 9.8 Hz), 4.40 (1H, dd, Jˆ9.6,
5.8 Hz), 3.77 (1H, dd, Jˆ18.0, 6.9 Hz), 3.40 (1H, dd,
Jˆ17.2, 6.8 Hz), 3.54±3.38 (2H, m), 3.17 (1H, ddd,
Jˆ9.8, 3.9, 1.0 Hz), 1.55 (3H, s), 1.32 (3H, s); MS (EI)
m/z 241 (M1, 2.2). Anal. calcd for C11H15O5N: C, 54.77;
H, 6.27; N, 5.81. Found: C, 54.48; H, 6.36; N, 5.74.
23
6.05±5.90 (1H, m), 5.78 (1H, d, Jˆ3.7 Hz); 5.28 (1H, dq,
Jˆ27.5, 1.6 Hz), 5.24 (1H, dq, Jˆ10.4, 1.6 Hz), 4.63 (1H, t,
Jˆ4.1 Hz), 4.40 (1H, dt, Jˆ7.1, 3.0 Hz), 4.23 (1H, ddq,
Jˆ12.6, 5.9, 1.2 Hz), 4.14±4.01 (4H, m), 3.90 (1H, dd,
Jˆ8.7, 4.4 Hz), 1.59, 1.46, 1.38 and 1.36 (4£Me, s); MS
(EI) m/z 285 (M12Me, 30.2). Anal. calcd for C15H24O6: C,
59.98; H, 8.05. Found: C, 60.09; H, 8.27.
3.1.13. 3-O-Allyl-1,2-O-isopropylidene-a-d-allofuranose
(16). Diacetonide 15 (3.00 g, 10 mmol) was dissolved in
90% aqueous acetic acid (30 mL) and the resulting solution
wasstirred for 24 h at rt. The mixture wasconcentrated in
vacuo, giving a yellow syrup that was ¯ash chromato-
graphed on silica gel (Et2O/hexane, 3:1) to yield the diol
16 (2.30 g, 90%) asa pale yellow ysrup: Rf 0.29 (Et2O/
3.1.16. b-tert-Butyldimethylsilyloxy-ulose 3. To a solution
of the isoxazoline 18 (130 mg, 0.54 mmol) in CH2Cl2/
methanol/AcOH (10 mL, 10:5:1) wasadded a catalytic
amount (10 mg) of Raney-Ni. The system was evacuated
and purged three timeswith the H 2 using a 3-way stopcock
with a H2 balloon. The mixture was then stirred vigorously
under H2 (balloon) at 258C for 3 h. CH2Cl2 (20 mL) was
added, and the solution was then dried over anhydrous
MgSO4 and ®ltered. The ®ltrate wasconcentrated under
23
hexane, 3:1); [a]D ˆ1108 (c 0.1, CHCl3); nmax(CHCl3)
1
3420 (OH) cm21; H NMR d 6.03±5.87 (1H, m), 5.27
(1H, d, Jˆ3.7 Hz), 5.33 (1H, dd, Jˆ22.4, 1.4 Hz), 5.27

7552
T. K. M. Shing, G. Y. C. Leung / Tetrahedron 58 (2002) 7545±7552
M.-W. J. Am. Chem. Soc. 1996, 118, 11311. (c) Yang, D.;
Wong, M. K.; Yip, Y. C.; Wang, X. C.; Tang, M. W.;
Zheng, J. H.; Cheung, K. K. J. Am. Chem. Soc. 1998, 120,
5943. (d) Yang, D.; Yip, Y. C.; Chen, J.; Cheung, K. K. J. Am.
Chem. Soc. 1998, 120, 7659.
reduced pressure to give b-hydroxy-ulose 19 that wasused
in the next stage without puri®cation. To a solution of the
b-hydroxy-ulose 19 in dry CH2Cl2 (30 mL), were added
imidazole (140 mg, 2.0 mmol), TBDMSCl (150 mg,
1.0 mmol) and a catalytic amount (10 mg) of DMAP. The
mixture wasstirred at rt for 12 h and then waspoured into
saturated NH4Cl (10 mL). The aqueousphase wasextracted
with CH2Cl2 (3£10 mL) and the combined organic extracts
were washed with brine (10 mL), dried (MgSO4), and
®ltered. Concentration of the ®ltrate followed by ¯ash chro-
matography (Et2O/hexane, 3:7) gave a white solid which
was recrystallized from EtOAc/hexane to give the ulose
the 3 (106 mg, 55% from 18) as white crystals: Rf 0.42
3. (a) Tu, Y.; Wang, Z. X.; Shi, Y. J. Am. Chem. Soc. 1996, 118,
9806. (b) Wang, Z. X.; Tu, Y.; Frohn, M.; Shi, Y. J. Org.
Chem. 1997, 62, 2328. (c) Wang, Z. X.; Shi, Y. J. Org.
Chem. 1997, 62, 8622. (d) Wang, Z. X.; Tu, Y.; Frohn, M.;
Zhang, J. R.; Shi, Y. J. Am. Chem. Soc. 1997, 119, 11224.
(e) Frohn, M.; Dalkiewicz, M.; Tu, Y.; Wang, Z. X.; Shi, Y.
J. Org. Chem. 1998, 63, 2948. (f) Wang, Z. X.; Shi, Y. J. Org.
Chem. 1998, 63, 3099. (g) Cao, G. A.; Wang, Z. X.; Tu, Y.;
Shi, Y. Tetrahedron Lett. 1998, 39, 4425. (h) Zhu, Y.; Tu, Y.;
Shi, Y. Tetrahedron Lett. 1998, 39, 7819. (i) Tu, Y.; Wang,
Z. X.; Frohn, M.; He, M.; Yu, H.; Tang, Y.; Shi, Y. J. Org.
Chem. 1998, 63, 8475. (j) Wang, Z. X.; Miller, S. M.;
Anderson, O. P.; Shi, Y. J. Org. Chem. 1999, 64, 6443.
(k) Wang, Z. X.; Cao, G. A.; Shi, Y. J. Org. Chem. 1999,
64, 7646. (l) Warren, J. D.; Shi, Y. J. Org. Chem. 1999, 64,
7675. (m) Tian, H.; She, X.; Shi, Y. Org. Lett. 2001, 3, 715.
(n) Tian, H.; She, X.; Xu, J.; Shi, Y. Org. Lett. 2001, 3, 1929.
4. (a) Solladie-Cavallo, A.; Bouerat, L. Org. Lett. 2000, 2, 3531.
(b) Armstrong, A.; Hayter, B. R.; Moss, W. O.; Reeves, J. R.;
Wailes, J. S. Tetrahedron: Asymmetry 2000, 11, 2057.
(c) Armstrong, A.; Hayter, B. R. Tetrahedron 1999, 55,
11119. (d) Carnell, A. J.; Johnstone, R. A. W.; Parsy, C. C.;
Sanderson, W. R. Tetrahedron Lett. 1999, 40, 8029. (e) Wang,
Z.-X.; Miller, S. M.; Anderson, O. P.; Shi, Y. J. Org. Chem.
1999, 64, 6443. (f) Adam, W.; Saha-Moller, C. R.; Zhao, C.-G.
Tetrahedron: Asymmetry 1999, 10, 2749.
23
(Et2O/hexane, 1:1); mp 108±1098C; [a]D ˆ271.4 (c 1.4,
1
CHCl3); nmax CHCl3) 1732 (CvO) cm21; H NMR d 5.84
(1H, d, Jˆ3.3 Hz), 4.77 (1H, t, Jˆ3.6 Hz), 4.59 (1H, dd,
Jˆ11.1, 7.2 Hz), 4.53 (1H, dd, Jˆ10.5, 1.5 Hz), 3.99 (1H,
dd, Jˆ10.8, 4.2 Hz), 3.73 (1H, dd, Jˆ11.1, 8.4 Hz), 3.63
(1H, t, Jˆ11.1 Hz), 3.48 (1H, dd, Jˆ10.2, 3.9 Hz), 2.91±
2.87 (1H, m), 1.60 (3H, s), 1.37 (3H, s), 0.84 (9H, s), 0.03
(6H, s); 13C NMR d 201.4, 114.3, 104.9, 83.7, 79.1, 76.6,
74.0, 58.3, 50.8, 26.3, 26.0, 25.7, 18.0, 25.6; MS (FAB) m/z
358 (M11H, 1), 301 (95), 243 (100). Anal. calcd for
C17H30O6Si: C, 56.95; H, 8.43. Found: C, 57.05; H, 8.08.
Acknowledgements
This research was supported by the CUHK Direct Grant.
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